1. Field of the Invention
This invention relates to a linear actuator using a piezoelectric member for producing accurate and micro linear movement.
2. Description of the Prior Art
In semiconductor and precision machinery industries there is an increasing need for providing an actuator that can producing a micro linear displacement down to nano meter (nm) level. However conventional actuators usually employ spring as braking means.
The spring force is generally not steady and difficult to achieve accurate micro movement. It is also not able to support large cutting force. FIGS. 1A and 1B show a conventional linear actuator which includes a front seat 2, a back seat 3, a first piezoelectric member 4 located in the front seat and a second piezoelectric member 5 located in the back seat. The actuator is mounted in a rail frame 1 which has a spring 6 located on one lateral side for controlling the linear feeding movement of the actuator. When in use, the second piezoelectric member 5 engages with two lateral sides at the rail frame 1, the first piezoelectric member 4 makes the front seat 2 to have frictional contact with the two lateral sides of the rail frame 1, the spring 6 provides additional friction force for this purpose.
The spring 6 also help to eliminate the gap between the front seat 2 and the rail frame 1. However the spring usually cannot sustain large cutting force (i.e., reacting force). The feeding motion and displacement is difficult to control. It is therefore difficult to achieve accurate movement and control.